The use of piezoelectric pickups for electric stringed instruments, such as electric guitars, is well known. Representative patents on this subject include U.S. Pat. Nos. 3,453,920 (Schere, 1969), 3,712,951 (Rickard, 1973), 4,356,754 (Fishman, 1982), 4,378,721 (Kaneko et al., 1983), 4,491,051 (Barcus, 1985), 4,501,186 (Ikuma, 1985), 4,567,805 (Clevinger, 1986).
In spite of the amount of effort by various persons and companies to develop a piezoelectric pickup for stringed instruments, the prior art devices have continued to be less than totally satisfactory. The inventor of the present invention has discovered that the "pressure sensitive" nature of standard piezoelectric pickups is inherently inconsistent with requirements of an ideal pickup. As will be described below, the present invention solves the primary problems of the prior art devices by using a pickup which is "bend sensitive" instead of "pressure sensitive".
Ideally, a pickup for stringed instruments should faithfully reproduce the vibrations of each string as a distinct electric voltage. In order to do this, the pickup should have the following properties:
1. The pickup for each string should be located close to the string so that no intervening structure modifies or filters the vibration of the string.
2. The pickup for each string should be properly oriented with respect to the principal plane of the string's motion, so that the pickup accurately senses the string's vibration.
3. The pickup for each string should be closely coupled to the string's motion, and should not pick up the vibrations of other strings.
4. The pickup should be part of the bridge of the instrument since that is where the vibrations are transmitted to the body of an acoustic instrument.
5. The pickup should allow the instrument's strings to be mounted in a normal fashion, i.e., to pass over a bridge with a small notch in it for each string, so that the player will be able to easily replace strings in the normal fashion for the instrument.
Clearly, these requirements or properties of an ideal pickup are somewhat overlapping.
The requirement that each pickup should sense the vibrations of only one string is, in part, derived from the MIDI specification for music synthesizer controllers, which requires that a separate input signal be provided for each sound generator in the synthesizer.
Most commercial pickups are deficient in one or more of these properties, which partially accounts for the well known differences in timbre between electronic and acoustic instruments. For example, the electromagnetic pickups used in standard electric guitars are not mounted on the guitar's bridge. In some cases they do not generate separate signals for each of the guitar's strings.
The prior art includes bridge mounted, piezoelectric pressure sensitive pickups for electronic violins, but these pickups are generally mounted far from the string, or in an orientation in which coupling to the string is marginal, or in a way which makes replacing the string awkward. In addition, the performance of these pressure sensitive pickups (i.e., the quality of the signals generated) is adversely affected by vibration of the entire pickup elements. For example, referring to FIGS. 1A and 1B, if the string 10 passes over a notch 12 in the bridge 14 of the instrument and a pressure sensitive pickup 16 is embedded (e.g., in a cavity 18 or 20) in the bridge 14, then the coupling will be unsatisfactory regardless of the orientation of the pickup element because the sound velocity in the bridge is so high that the transmitted string vibration will cause the entire pickup element to vibrate rather than putting vibratory pressure on the pickup element. If the pickup is placed under one foot of the bridge, it is so far from the string that the bridge structure will filter the string's vibration in an unsatisfactory manner, attenuating important high frequency components of the string's vibration.
Referring to the plan view of a violin or cello pickup shown in FIG. 1C, one method of properly coupling a string 10 to a pressure sensitive pickup 22 which was considered by the inventor before developing the present invention is to have the string 10 press against the pickup itself in an orientation where the string vibrations are normal to the pressure sensitive surface of the pickup. In FIG. 1C, a pickup assembly 21 for one string is shown, positioned on the instrument's bridge 14. Pressure sensitive piezoelectric element 22 is encased in cylindrically shaped hard plastic member 24 that is held in place by an aluminum support 26. The string 10 presses up against the pickup assembly 21 at all times, and vibrations of the string 10 directly translate into pressure changes in the piezoelectric element 22. While this enables the pickup to provide a good waveform, the string 10 must bend slightly where it crosses the pickup so that the tension in the string will press it against the pickup 21. Arranging the bridge 14 and the tailpiece 30 for holding the end of the strings to produce such a bend in the strings makes it awkward to mount the string on the instrument and causes problems in tuning the string.
The present invention is premised on the observation that the prior art piezoelectric pickups use pressure sensitive elements, and that it is difficult to properly couple the string vibrations of a bowed or plucked string instrument to these pressure sensitive elements. From one perspective, pressure sensitive elements are inherently unsatisfactory because the nature of the tones and sounds generated by the strings in stringed instruments is vibratory, not fluctuating pressures.
It is therefore a primary object of the present invention to provide a pickup for stringed instruments which s directly responsive to the vibrations of the instrument's strings. Another object of the present invention is to provide a pickup which produces an independent electrical signal for each string of an instrument.